This page now includes just the basic free version of the ImagePaste plugin. Following versions have been renamed to SimpleUploads, that plugin isn't free and includes lots of features that aren't available in this one.
This plugin takes care of images pasted or dropped in Firefox to convert them to uploaded files and avoid the problems caused by embedding huge base64 images into a page (no separate caching, worse performance, incompatibility with some mail clients, some servers might strip them out when you try to save them, problems trying to edit those images in CKEditor....)
You just need to have a QuickUploader configured in CKEditor and add this plugin, then it will take care of convert the pasted images with Firefox into normal files stored at your server.
Again: This plugin is targetted only at Firefox, it takes the base64 data-encoded URI images and converts them into normal files.